Only shitposters want the thread to split.
The one time we actually tried a split (many years ago), it just made it harder to talk about iDOLM@STER, and easier for shitposters to claim that "LOOK, IT'S -THEM- FROM THE OTHER THREAD. THEY ARE THE ONES CAUSING TROUBLE", while referring to their own posts.
Branchwarring and parasocial fanfiction are also really bad. You have to be a really stupid and awful person to spend all your time engaging in such negative behavior.